Catapult launcher



Dec. 24, 1963 A, c .uscURLocK 3,115,004

CATAPULT LAUNCHER Filed June 30, 1952 4 Sheets-Sheet 1 IN VENTOR ra/ l.Jalal/w15' AGENT Dec. 24, 1963 Filed June 30, 1952 PRESSURE A. C.SCURLOACK CATAPULT LAUNCHER 4 Sheets-Sheet 2 PBWn-s'z gunna:

ra/v Jams/704% Assur Dec. 24, 1963/ A. c.- scuRLocK 3,115,004*

vCA'IAPULT LAUNCHER l Filed June 30, 1952 4 Sheets-Sheet 3 AVERAGEACCELERATION n: [2g 50o lbs DEAD LOAD IOO ,INVENTOR l'e Javi/M1 AGENTUnited States Patent O "ice 3,115,004 CATPULT LAUNCHER Arch C. Scurlock,Fairfax, Va., assigner to Atlantic Research Corporation, Alexandria,Va., a corporation ori Virginia Filed lune 30, 1952, Ser. No. 296,331 2Claims. (Cl. oli-26.1)

This invention relates to an improved catapult device for launchingplanes or missiles.

The conventional catapult, in which the pressure in the combustionchamber is substantially the same as that in the catapult tube,possesses a number of disadvantages. Powder charges for such catapultscan be designed so that the same charge can automatically launch varyingdead weights to substantially the same acceleration. Ir" a change in theacceleration is desired, however, a different charge must be employed.

Another dificulty stems from the fact that it is sometimes desirable tomaintain catapult tube pressures at levels below those at which manypropellants will burn reliably. Although certain double-base propellantscan be produced which will burn successfully at pressures down to about3G() p.s.i., the range of propellant choice is greatly limited and, insome cases, it may be desirable to operate at even lower pressures inthe catapult or piston tube.

The object of this invention is to provide catapult launchers which aredesigned in such a manner that they permit the launching of differentdead loads at any desired acceleration within a range with the samepropellant charge.

Still another object is to provide catapult launchers which can operatesuccessfully with substantially any type of propellant powder charge,including those which require high pressures for reliable combustion.

Other objects and advantages will become obvious from the drawings andthe following detailed description.

FIGURE l is a diagrammatic view of a longitudinal section through thecatapult showing the essential features of the invention.

FIGURE 2 is a cross section taken along line 2-2 of FIGURE 1.

FIGURE 3 is a graph illustrating the relationship between combustionchamber pressure and orifice cross sectional area for a given propellantcharge.

FIGURE 4 is a graph illustrating the relationship between orice crosssectional area and dead load for a given acceleration.

FIGURE 5 gives catapult performance curves for a given dea-d load andshows variation in acceleration and piston chamber pressure at differentoriiice cross sectional areas.

The catapult of my invention comprises a combustion chamber whichcommunicates with the catapult or piston chamber through a smalloriiice, the throat area of which may be varied in any desired manner.As shown in the drawings, the combustion chamber is large enough tocontain the solid propellant charge and, while providing some freevolume, the free volume is substantially small relative to the size ofthe propellant charge. By reducing communication between the chambers toa small oriice for passage of the combustion gases, high pressures3,ll5,@04 Patented Dec. 24, 1963 are maintained in the combustionchamber and relatively low pressures in the piston chamber.

In the drawings, 1 is the combustion chamber and 2 the propellantcharge. The piston 4 is located in the catapult chamber 3. The walls 5of the combustion chamber should be heavy enough to withstand the highpressures. Because of the lower pressures maintained in it, the walls 6of the catapult chamber need not be as thick as those of the combustionchamber. The combustion gases pass from the combustion chamber into thepiston chamber by way of a small oriiice 7. The cross sectional area ofthe orice may be varied as desired by any suitable means, as forexample, by gate valve 8, which may be inserted into the orice orwithdrawn by screw 9. The screw may be calibrated so that the Valve maybe set for the desired orifice area. The valve may be recessed into slotitl until end Il is ush with the orifice wall. It will be understoodthat any suitable means for varying the cross sectional area of theoriiice may be employed.

By providing an orifice of sutliciently small maximum throat area,substantially any pressure within the relatively low range desirable forcatapult propulsion may.

be maintained in the piston chamber while high pressures which ensurethe rapid and reliable combustion of the propellant grain are maintainedin the combustion chamber. A maximum oritice area from about 1 tenthousandth to 1 hundredth of the cross sectional area of the catapulttube is generally satisfactory for most purposes. However, the orificemay be proportionally larger or smaller depending on such factors as thedesired differential in pressure between the two chambers and the like.

By varying the throat area of the oriiice, the pressure in thecombustion chamber and the corresponding pressure in the piston chambercan be controlled and varied in such a manner that different dead loadscan be moved at any desired acceleration with the same propellantcharge. In other words, the same dead load may be launched at differentaccelerations; different loads may be launched at the same acceleration;and both the load and the acceleration may be varied. The orice crosssectional area is set at the predetermined size prior to combustion ofthe charge and remains in this position until launching of theparticular load is completed.

Decreasing the throat area of the orice causes an increase in pressurein the combustion chamber which, in turn, causes a marked increase inburning rate of the propellant charge. The resulting increase incombustion chamber pressure is considerably larger proportionately thanthe decrease in orilice throat area. Neglecting such minor factors asthe density of the propellant gas and the free volume in the combustionchamber, the relationship between the pressure in the combustion chamberand the oriiice throat area may be expressed as follows:

1 P 1 ati-.i

where Pc is the pressure in the combustion chamber, A, is the orificethroat area and n is the burning law pressure exponent for theparticular propellant composition used. In the case of the usualpropellant having a burning law pressure exponent of about 0.5, therelationship is ap- In other words, reducing the throat orifice area byhalf produces approximately a four fold increase in combustion chamberpressure. Doubling the throat orifice area decreases the chamberpressure to approximately one fourth of its original value.

In the case of a propellant charge having a burning law pressureexponent which is less than 0.5, the Value of the exponent will begreater than 2. Where the burning law pressure exponent is higher than0.5, the value of will be correspondingly lower. Since the value of lzfor any practical propellant charge is always less than 1, the value ofis always higher than l.

It would appear that the decrease or increase in orifice throat areacauses a corresponding and directly proportional decrease or increase,respectively, in the mass flow rate of the powder gases from thecombustion chamber into the piston chamber. The relationship between themass flow rate of the powder gases m, the pressure in the combustionchamber Pc, and the orifice throat area At is as follows:

m=CDPcAt where the constant of proportionality CD is known as the nozzlecoeticient.

However, since the combustion chamber pressure increases or decreases ata considerably greater rate than the corresponding decrease or increasein orice throat area, substituting the values of Pc for dilferent valuesof At results in a net overall increase or decrease in the mass flowrate of the powder gases for decreased or increased values of At,respectively. Increasing the mass flow rate of gases increases theeffective pressure in the piston chamber and, conversely, decreasing themass flow rate of the gases through the orice decreases the effectivepressure in the piston chamber.

For the case of constant acceleration, the equation of motion is asfollows:

where P is the pressure in the piston tube, W is the effective grossweight of load in motion, a is piston acceleration, A is the crosssectional area of the catapult tube and g is the conversion factor frompounds of force to poundals (32.2 poundals/1b.). Thus an increase in thepressure in the piston chamber may be utilized to increase theacceleration for a given load, to move a larger load at the sameacceleration or to vary both the load and the acceleration. Conversely,a decrease in piston chamber pressure may be utilized to decrease theacceleration for a given load, to move a lighter load at the sameacceleration or to vary both factors.

The equation which relates conditions in the combustion chamber withthose in the piston chamber is as follows:

PAat NRTCDAL gas per unit mass, R is the gas constant and T is the gastemperature in the piston chamber. Substituting will Ag for P,

z lVa'lt NRTCD/ltg The latter equation shows that the pressure in thecombustion chamber is proportional to the weight of the load times thesquare of the acceleration and that these two factors may be varied asdesired by changing the combustion chamber pressure. Since thecombustion chamber pressure may be controlled in a predetermined mannerby varying the orifice cross sectional area, it will be seen that, bychanging the latter, different dead loads may be launched at any desiredacceleration with the same propellant charge.

Practical limitations are imposed by the sufficiency of the charge orits economical utilization. The weight of the load and acceleration maybe increased to the point where the given propellant charge may beconsumed bcfore the piston has travelled the full length of the tube.Under these conditions a larger charge with an increased availableburning distance would be desirable. On the other hand, the load andacceleration may be reduced to the point of such incomplete utilizationof the charge as to cause an undue amount of waste of propellantmaterial. In such a case, a smaller charge with a decreased availableburning distance would be more economical.

FIGURE 3 shows the relationship between orifice cross sectional area andcombustion chamber pressure for a given propellant charge. Thepropellant employed in this case has a burning law pressure exponent ofabout 0.5. The considerably greater rate of change in combustion chamberpressure as compared with the rate of change of orifice cross sectionalarea is clearly illustrated. The powder grains used were designed forideal operation with a dead load of lbs., an orifice cross sectionalarea of 0.019710 in?, an initial gas pressure in the combustion chamberof 0 p.s.i. and a nal gas pressure of 20,000 p.s.i.

FIGURE 4 illustrates the changes in orifice throat area required to givethe same average acceleration to different loads while using the samepowder charge.

FIGURE 5 gives the performance curves for a catapult operating with agiven weight load of 150 lbs. at different orifice throat areas and thesame powder charge. It shows the increase both in piston chamberpressure and in load acceleration obtained by decreasing the size of theorifice and vice versa. The powder grains employed here are the same asthose used in FIGURE 3.

A comparison of the combustion chamber pressures as shown in FIGURE 3and the piston chamber pressures as shown in FIGURE 5 clearlyillustrates the relatively low pressures which may be maintained in thepiston chamber while high pressures, which ensure reliable burning ofthe propellant at a high combustion rate, are maintained in thecombustion chamber by means of the reduced orifice. Thus substantiallyany type of propellant charge, regardless of the pressures required forreliable combustion, may be employed in the highlow pressure catapult.

An important advantage of the high-low pressure catapult stems from thefact that it does not require propellant grains designed to give suchhigh progressivity as those required by the conventional catapult sothat standard perforated grains may be adequate for ecient operation ofthe former.

Although this invention has been described with reference toillustrative embodiments thereof, it will be apparent to those skilledin the art that the principles of this invention may be embodied inother forms, but Within the scope of the appended claims.

Iclaim:

1. In a catapult launcher, means forming a combustion chamber for asolid propellant charge, the combustion chamber being characterized by asubstantially small free volume relative to the propellant charge, andmeans forming a piston chamber, said combustion chamber opening directlyinto said piston chamber through a restricted orice having a maximumcross sectional area which is substantially smaller than that of saidcombustion chamber, and a valve which is operable to adjust said orificeto a predetermined cross-sectional area prior to combustion and whichremains fixed throughout the launching cycle.

2. The catapult launcher of claim 1 in which the orifice has a maximumcross-sectional area which is about one hundredth of the cross-sectionalarea of the combustion chamber.

References Cited in the lle of this patent UNITED STATES PATENTS1,161,744 Sparre Nov. 23, 1915 1,535,475 Jeansen et al Apr. 28, 19251,935,123 Lansing Nov. 14, 1933 2,289,318 Pratt July 7, 1942 2,289,766Fieux July 14, 1942 2,555,333 Grand et al June 5, 1951 2,670,596Whitworth Mar. 2, 19,54 2,723,528 Stark Nov. 15, 1955 FOREIGN PATENTS441,053 Great Britain Jan. 6, 1936

1. IN A CATAPULT LAUNCHER, MEANS FORMING A COMBUSTION CHAMBER FOR ASOLID PROPELLANT CHARGE, THE COMBUSTION CHAMBER BEING CHARACTERIZED BY ASUBSTANTIALLY SMALL FREE VOLUME RELATIVE TO THE PROPELLANT CHARGE, ANDMEANS FORMING A PISTON CHAMBER, SAID COMBUSTION CHAMBER OPENING DIRECTLYINTO SAID PISTON CHAMBER THROUGH A RESTRICTED ORIFICE HAVING A MAXIMUMCROSS SECTIONAL AREA WHICH IS SUBSTANTIALLY SMALLER THAN THAT OF SAIDCOMBUSTION CHAMBER, AND A VALVE WHICH IS OPERABLE TO ADJUST SAID ORIFICETO A PREDETERMINED CROSS-SECTIONAL AREA PRIOR TO COMBUSTION AND WHICHREMAINS FIXED THROUGHOUT THE LAUNCHING CYCLE.